1. Field of the Invention
The invention relates to testing of integrated circuits using probe cards, and more particularly to bottom side stiffeners for probe cards used in production testing of wafers containing imaging die.
2. Description of the Related Art
Semiconductor integrated circuits (ICs) are produced extensively and are used in a vast number of products. As semiconductor ICs become increasingly smaller and production levels increase, testing of the ICs becomes more difficult, and more critical.
ICs are mass-produced on round, thin sheets of semiconducting material referred to as wafers. Wafers most commonly are made of silicon. Anywhere from 50 to 200 or more identical circuits, or die, can be produced in a single wafer. Each circuit is provided with contacts, such as peripheral pads, to connect the circuit die with other components or circuits. Testing devices need to make connections with the circuits of each individual die by engaging the contacts. Rather than testing each die on a wafer one at a time, the testing devices typically test several die at once. All of the die are tested by moving the wafer under test relative to the fixed probe card of the testing device in a sequential testing pattern. On a wafer with 200 circuit die, for example, a testing device that tests four die at once will use a pattern of at least 50 moves to cover the entire wafer. Thus, the connections made by the probes on a probe card of a testing device with the die contacts must be made repeatedly and reliably for each of hundreds of wafers in a production batch, for example.
In addition to making reliable connections with each die, active testing of imaging die also requires illuminating each die using a light source. In order to achieve consistent active testing from die to die and wafer to wafer, the illumination must be constant and evenly distributed onto each of the several die being tested. In the example above, for instance, the illumination provided to each of the four die being tested simultaneously must be as consistent as possible. In the past, stiffeners provided on the top side of probe cards for imaging die have contributed to inconsistent lighting during testing, which has lead to inconsistencies and false-negative results.
Thus, there is a need and desire for a probe card for imaging die provided with a stiffener which allows consistent lighting of the imaging die during active production testing.